The invention relates to a transponder, for use in a communication system for receiving and transmitting electro-magnetic signals.
Generally, the invention is concerned with a transponder for use with at least two communication terminals and capable of relaying communications between the communication terminals optimally in order to minimize the frequency band width allocations and possible interference between the communication terminals.
It is known that two communication terminals, each having an antenna array, can be used to obtain retrodirective oscillating loops for focusing the respective antenna arrays even for noise signals. In this connection, reference is had to applicant's U.S. Pat. Nos. 3,757,335 and 4,001,691, as well as his co-authored article entitled, "Self-Directional Micro-wave Communication System", I.B.M. Journal of Research and Development, March, 1974 pages 149 to 163.
Generally, a retro-directive oscillation loop between two communication terminals features the transfer of electro-magnetic energy from one communication terminal through space to the other communication terminal, where the electro-magnetic signal is amplified and transmitted back to the first communication terminal where it is again amplified and re-transmitted and this process continues idefinitely. If the total loop gain is greater than the total loop loss, there will be a build-up signal even without the initial transmission of a carrier.
In particular, the disclosure in applicant's Pat. No. 4,001,691, issuing Jan. 4, 1977 is incorporated herein by reference.
The Abstract of the Pat. No. 4,001,691 is as follows:
In an electronic system for use in a communication system wherein there is radiated a plurality of information carrying electro-magnetic first signals each having a radiated source and each having a radiated electro-magnetic first reference signal, a transponder operable for receiving all of the electro-magnetic signals and for radiating a response thereto, a plurality of information carrying electro-magnetic second signals corresponding respectively in information to the first signals and a plurality of electro-magnetic second reference signals corresponding respectively to the first reference signals, the transponder comprising a plurality of first antenna means each having output means and each operable for receiving the first signals and the first reference signals, and for producing in response thereto a set of corresponding transmission line signals at its output means, and transmission means coupled to the output means of all of the first antenna means and operable for producing from the sets of transmission line signals a second reference signal, as well as the second signals, each of the second signals having a spatial electro-magnetic power density distribution having a peak value in the direction of each of the sources except for the source of its corresponding first signal for sources angularly spaced apart with respect to the transponder.
The main claim of the Pat. No. 4,001,691 is essentially the same as the Abstract given above and one of the dependent claims includes the limitations of at least three first antenna means, and the transmission means comprising de-phasing means coupled to the output means of one of the first antenna means and operative for producing from the set of transmission line signals from one of the first antenna means a plurality of de-phased signals corresponding, in information content respectively to the first signals, each of the de-phased signals having an electrical phase substantially independent of the position of the radiating source of its corresponding signal, and processing means and the other of the first antenna means operative for receiving the de-phased signals and the respective set of transmission line signals for producing the second signals.
Although retro-directive oscillating communication systems are of considerable interest, there is also considerable interest in a transponder capable of redirecting electro-magnetic transmissions and minimizing the band width requirements by automatically re-transmitting signals to optimize communication while minimizing electro-magnetic interference.